1. Field of the Invention
The present invention relates to a multi-chamber apparatus which is suitable for formation of contact holes, for example, in the semiconductor device manufacturing process and a method of manufacturing a semiconductor device.
2. Description of the Related Art
Improvement in packing density of VLSI requires further miniaturization of contact holes for electrically connecting a semiconductor substrate and wirings formed thereon and via holes and through holes for electrically connecting multilayer interconnections. In the 0.25 .mu.m rule, the aspect ratio of these contact holes, via holes or through holes (hereinafter generally called a connecting hole) is larger than 2. In general, as shown in a partial schematic cross-sectional view of FIG. 1A, a connecting hole can be formed by forming an insulating layer 7 on a semiconductor substrate 1 or a lower wiring layer and thereafter forming an aperture 8 in the insulating layer 7. The reference numeral 2 denotes an element isolating region; 3, a gate oxide film; 4, a gate electrode; 5, an LDD side wall; 6, a source drain region. Thereafter, a metal wiring material film 9 is formed on the insulating layer 7 including the inside of the aperture 8, for example, with the sputtering method. Thereby, the aperture 8 is filled with the metal wiring material film 9 to complete a connecting hole.
However, when the aspect ratio of the aperture 8 is high, a problem rises here that the metal wiring material is not deposited on at the bottom part of the aperture 8 due to the shadowing effect or that the metal wiring material film is not formed in the sufficient thickness at the side wall of aperture near the bottom part thereof (refer to FIG. 1B). The shadowing effect means a phenomenon that the incident sputtering particles are not deposited on a part so-called an optically shadowed portion of the aperture during the sputtering process. If such problem is generated, reliability for electrical connection of a connecting hole is degraded and connection failure occurs in the connecting hole in the worst case.
A high temperature sputtering method is a typical technology for covering the side wall of an aperture having a high aspect ratio with aluminum or aluminum system alloy (hereinafter called by the general name of Al system alloy). This high temperature sputtering method is effective for heating a semiconductor substrate 1 up to about 500.degree. C. on the occasion of forming a film of the Al system alloy with the sputtering method. As explained above, when the semiconductor substrate 1 is heated, the Al system alloy deposited on the insulating film 7 is fused to become fluid and flows into the aperture 8. As a result, the aperture 8 can be surely filled with the Al system alloy.
Cu or its alloy has a lower resistance than the Al system alloy and shows excellent resistance for electro-migration (EM resistance material). Therefore, Cu or its alloy is very attractive material for future high integration and high-speed semiconductor device. Characteristics of Cu, Ag, Au will be shown in the following table.
High Specific Melting Tensile temp. resistance point strength EM sputtering/ (.mu..OMEGA.cm) (.degree. C.) (kgf/mm.sup.2) resistance applicability Al 3.2 650 4.8 .DELTA. .largecircle. system alloy Cu 1.7 1083 21.7 .largecircle. x Ag 1.6 961 12.7 .DELTA. x Au 2.3 1063 13 .DELTA. x W 10 3380 60 .circleincircle. x
In the above table, ".circleincircle." means very excellent characteristics, ".largecircle." means excellent characteristics and ".DELTA." means a little lower characteristics than ".largecircle.". Cu, Ag and Au have a lower specific resistance and therefore are suitable for realizing high-speed operation of a semiconductor device. Meanwhile, Cu has excellent characteristics for electro-migration resistance and moreover it can be expected to also have excellent stress migration resistance because it has a tensile strength about five times higher than that of Al system alloy. However, Cu, Ag, Au respectively have the melting point as high as about 1000.degree. C. Therefore, it is impossible to bury the aperture with such metal materials using the high temperature sputtering method where a semiconductor substrate is heated up to about 500.degree. C.
In recent years, investigations are continued for reflow method where a semiconductor substrate is heated, after a metal wiring material is deposited on an insulating layer, to fuse the metal wiring material deposited on the insulating layer to become fluid and thereby the aperture can be filled with a film of metal wiring material. Use of such reflow method enables that a high melting point metal wiring material such as Cu is fused to become fluid and thereby the aperture can be buried with a film of the high melting point metal wiring material. Such reflow technology is disclosed, for example, in the reference titled as "Reflow Characteristic of Sputtered Cu Film", p. 769, 29p-ZE-3, Proceedings of the 54th Applied Physics Society of Japan (Autumn). However, in this technology, since the time required for reflow process is as long as 30 minutes, if 25 semiconductor substrates are processed by the single wafer processing type reflow apparatus of the related art, total time of about 13 hours is required and it is too low in the productivity. If the reflow time is shortened, Cu does not reflow into the aperture and voids are generated therein.
In the reflow method, atoms forming a metal wiring material diffuses as the surface and the metal wiring material flows into the aperture when the semiconductor substrate is placed under the heat treatment while the surface condition of the sputtered metal wiring material is cleaned under the vacuum condition. Therefore, if a semiconductor substrate is exposed to the atmospheric condition before execution of the reflow process or is left under the low vacuum environment, an oxide film is formed at the surface of the metal wiring material and it does not flow into the aperture even when the reflow process is executed. For example, it is described in the reference entitled as "Burying by Al Reflow under Ultra-high Vacuum Condition", p. 720, 30a-ZY-8, Proceedings of the 40th Applied Physics Society of Japan (Spring). This reference relates to the technology of aluminum reflow and moreover to a conventional short term reflow process of about 180 seconds.
As explained above, the technology for executing the reflow process to the sputtered Cu film with a single wafer processing type reflow apparatus and the technology for improving the burying characteristic by the aluminum reflow under ultra-high vacuum condition are already known from the references listed above, but so long as the applicant of the present invention has searched, the technology for certainly forming a connecting hole in a semiconductor device with a high productivity using a high melting point metal wiring material such as Cu without deteriorating a throughput is not yet obvious. That is, when a contact hole is to be buried by reflow process of a high melting point material such as Cu, Ag, etc., the process can be stably achieved by raising a temperature or extending the heat treatment time. However, in the former case of raising the temperature, the material, for example, Cu, must be set to the temperature of about 600.degree. C. Under such a high temperature, Si barrier metal easily diffuses into Si. Therefore, in such a reflow process, the latter method is inevitably employed, that is, the heat treatment time is extended. Since the multi-chamber apparatus combining the sputtering apparatus and reflow chamber has employed the single wafer processing mode for processing the wafers one by one, an actual reflow time becomes longer giving adverse effect on the throughput. Therefore, even if a connecting hole is formed with the technologies disclosed in above references by combining the sputtering apparatus and batch type reflow apparatus of the related arts, an oxide film is formed at the surface of the high melting point metal wiring material such as Cu, etc. and the high melting point wiring material does not flow into the aperture when the reflow process is performed to the high melting point metal wiring material such as Cu at the temperature considerably lower than the melting point thereof.